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Astron. Astrophys. 341, 216-223 (1999)


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On the magnetic field and circumstellar environment of the young O7 star [FORMULA]1 Orionis C *

J.-F. Donati 1 and G.A. Wade 2

1 Laboratoire d'Astrophysique, Observatoire Midi-Pyrénées, F-31400 Toulouse, France (e-mail: donati@obs-mip.fr)
2 Department of Physics and Astronomy, University of Western Ontario, London Ontario, N6A 3K7, Canada (e-mail: gwade@astro.utoronto.ca)

Received 23 July 1998 / Accepted 6 October 1998

Abstract

We present new circular spectropolarimetric observations of the young O-type star [FORMULA] Orionis C obtained with the MuSiCoS échelle spectropolarimeter and the 2 m Télescope Bernard Lyot, in an attempt to detect the surface magnetic field structure invoked to explain the periodic variability of [FORMULA] Ori C at X-ray, UV and optical wavelengths. We obtain null detections with 250 G 1[FORMULA] error bars for the disc-averaged line-of-sight (i.e. longitudinal) component of the surface magnetic field vector, from which we conclude that the polar strength of the dipole field structure is lower than 1.6 to 2.0 kG (with a confidence level of 87%), depending on the exact orientation of the magnetic and rotation axes with respect to the line of sight.

We report as well the unexpected discovery of strong, time variable continuum circular polarisation in the spectrum of [FORMULA] Ori C, as well as depolarisation structures associated with nebular emission lines, indicating that this continuum polarisation (the nature of which is as yet unclear) is produced within the immediate circumstellar environment.

Key words: polarization – stars: circumstellar matter – stars: early-type – stars: individual: 1  Ori C – stars: magnetic fields

* Based on data collected with the MuSiCoS spectropolarimeter of the Télescope Bernard Lyot, Observatoire du Pic du Midi, France

Send offprint requests to: J.-F. Donati

© European Southern Observatory (ESO) 1999

Online publication: November 26, 1998

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